Process and compositions for treating aluminum and aluminum alloys

ABSTRACT

ALUMINUM AND ALUMINUM ALLOY SURFACES ARE PREPARED FOR METAL FINISHING OPERATIONS SUCH AS ANODIZING, PAINTING, BRIGHT DIPPING ETC., BY IMMERSING THEM FOR ABOUT 1 TO ABOUT 10 MINUTES AT A TEMPERATURE OF ABOUT 60* TO ABOUT 170*F. IN AND ACIDIC SOLUTION OF A PEROXYDIPHOSPHATE COMPOUND, SUCH AS POTASSIUM PEROXYDIPHOSPHATE. OPTIONALLY, THE SOLUTION MAY ALSO CONTAIN A FLUORIDE SALT.

3,634,262 PROCESS AND COMPOSITEONS FOR TREATING ALUMINUM AND ALUMINUMALLOYS John J. Grunwald, New Haven, and Edmund E. Homer,

Watertown, Conn., assignors to MacDermid, Incorporated, Waterbury, Conn.No Drawing. Filed May 13, 1970, Ser. No. 37,013 Int. Cl. (311d 7/54 U.S.Cl. 252-100 15 Claims ABSTRACT OF THE DISCLOSURE Aluminum and aluminumalloy surfaces are prepared for metal finishing operations such asanodizing, painting, bright dipping etc, by immersing them for about 1to about 10 minutes at a temperature of about 60 to about 170 F. in anacidic solution of a peroxydiphosphate compound, such as potassiumperoxydiphosphate. Optionally, the solution may also contain a fluoridesalt.

This invention relates to the surface preparation of aluminum andaluminum alloys for subsequent metal finishing operations such aspainting, anodizing, plating bright dipping, Welding, chromating, etc.More particularly, this invention relates to novel acidic compositionscontaining ammonium peroxydiphosphate or peroxydiphosphates of thealkali metals and the alkaline earth metals and to a process fordeoxidizing and desmutting aluminum surfaces subsequent to the finalmetal finishing operation.

It is an important procedure in the aluminum finishing industry, priorto the finishing operations mentioned above, to remove the ever-presentoxide film which forms on the surface of aluminum alloys on atmosphericexposure. A typical method employed in the past by which this isachieved is to immerse the previously degreased aluminum object in asuitable deoxidizing solution, which usually contains oxidizing agentssuch as chromic acid, chromates or dichromates, nitric acid or a mixtureof these materials in Well defined proportions. Their function is toreplace this tenacious oxide film on the aluminum alloy by another filmmore suitable for subsequent treatments.

The use of chromic acid or any other chrome base deoxidizing solution inthe finishing industry creates waste disposal difficulties since theseformulations must be treated chemically before they can be disposed ofsafely. Also the use of chromic acid in certain finishing shops maycause contamination of rinsing Waters, bright dips, anodizing andplating solutions. Furthermore, the use of nitric acid is alwaysaccompanied by obnoxious fumes which makes for uncomfortable and healthhazardous conditions as well as corrosive action in many platinginstallations.

Another procedure frequently used heretofore in the aluminum finishingindustry as a preparatory step, prior to the finishing treatments,consists of etching the aluminum alloy in a suitable alkaline solution,thereby removing substantial amounts of surface metal. During thisetching process, certain alloying elements of the aluminum, which areinsoluble in the etching solution, will cover the surface in the form ofa loose coating forming an unsatisfactory basis for further treatment,and care must therefore be taken to see that this loose coating iscompletely removed. This phenomenon is known in the industry as smutformation, and removal of the smut is also covered by the termdeoxidizing as it is used in practice and in the present specificationand appended claims.

3,634,262 Patented Jan. 11, 1972 It is therefore a primary object ofthis invention to provide a novel deoxidizing solution which is free ofwaste treatment difliculties and wherein the ingredients are readilycontrollable at the room operating temperature of the solution; also toprovide a solution compatible with bright dip and anodizing solutions.It is a further object of the invention to eliminate adherent films onthe articles undergoing treatment and the production of offensive fumesand insoluble residues in the bath, which disadvantages have inherentlycharacterized prior aluminum deoxidizing and desmutting operations.Among other advantages of the treatment herein disclosed is the factthat the bath components used are physiologically safe, Which makes themWell suited for treating aluminum objects to be used in the foodindustry. It is found that the deoxidizing action of the novel bathcomposition here disclosed is considerably faster than other existingproprietary deoxidizers. Other features and advantages of the inventionwill .be discussed as the description proceeds.

As previously pointed out, the novel deoxidizing and desmuttingcompositions of this invention contain at least one peroxydiphosphatecompound which by itself in aqueous solution regardless of theconcentration will not perform as a deoxidizer or deoxidizer-desmutterof aluminum or aluminum alloys. Surprisingly, the novel deoxidizing anddesmutting solutions of this invention which comprise aqueous solutionsof a peroxydiphosphate compound selected from the group consisting ofammonium peroxydiphosphate, an alkali metal peroxydiphosphate and analkaline earth metal, and certain acids or acid salts thereof insufficient amount to provide a solution pH of not over 3.0, areexcellent deoxidizing and desmutting compositions. The concentration ofthe peroxydiphosphate compound which can be varied over a wide rangegenerally will be from about 18 grams per liter up to saturation. Suchsolutions provide excellent deoxidizing and desmutting action onaluminum and all aluminum alloys with the exception of those alloyshaving a high silicon content. These novel aqueous solutions areespecially useful in deoxidizing and desmutting wrought aluminum andWrought aluminum alloys. Further, it has been found that casting alloyswith silicon content not in excess of 1%, can be handled with these samesolutions provided a fluoride anion is included as one of theingredients.

In the deoxidizing-desmutting process of this invention, theperoxydiphosphates react with the aluminum or its alloying elements andare reduced to the orthophosphates. Thus, the bath after beingexhausted, can be conveniently disposed of after neutralization as inthe case of any other spent acid solution.

Furthermore, introduction of a suitable wetting agent such as any of thewell-known surface tension depressing ionic or nonionic materials, isfound to be of great assistance in removing oxide films from aluminumstrip processed in continuous operation, wherein the aluminum strip ismoved at high speed through a trough containing the deoxidizing solutionand then through a rinsing trough. Large quantities of aluminum stripcan be processed during short periods of time in such manner. Suchtreatments are impossible with chrome type deoxidizers which requirevery abundant rinsing that cannot .be provided in a continuousoperation.

Another advantage of this formulation is that it will not dimensionallalter or aflect aluminum objects that are immersed, even for veryprolonged periods of time.

Alkali metal peroxydiphosphates which can be employed in formulating thenovel solutions of this invention include sodium, potassium and lithiumperoxydiphosphates while the useful alkaline earth metalperoxydiphosphates include calcium and magnesium.

As previously pointed out it is sometimes advantageous add a fluorideanion to the novel solutions of this inention and this is especiallytrue with regard to alumiium alloys which contain a considerable amountof silicon such as Type 6061, 6063, etc. A wide variety of solubleiuoride compounds canbe employed although it is preferred to utilize afluoride compound selected from the group consisting of NaF, Natl-1P NHHF Na siF HF, FIBF KF, KHF NaHF NH P, K SiF Fel and mix- :ures thereof.Generally, 'sufiicient soluble fluoride comaound is added to provide afluoride ion concentration in :he aqueous solution of from 0 to about 6grams per liter.

Acids useful in preparing the novel compositions of his inventioninclude sulfuric, phosphoric, sulfamic, and nixtures thereof; acid saltsof these same acids, such as lOdlllIl'l bisulfate, potassium bisulfateand mixtures there- )f. Preferably, the acid used in preparing the noveldexidizing solutions is sulfuric acid. Sufiicient acid, acid .alt, or amixture of these two materials is added to the iovel bath composition toprovide a pH of not more than L0.

A complete deoxidizing process for aluminum and aluninum alloysutilizing the novel acidic aqueous peroxyliphosphate solutions of thisinvention together with the isual cleaning and etching steps is asfollows:

PROCESS I '1) 3 to 5-minute immersion in a non-etch aluminum soakcleaner at a concentration of 8 to 10 oz./ gal. and at 160 to 180 F.,

:2) 30-second cold water rinse,

:3) 1 to 3-minute immersion in an alkaline etchant at a concentration of8 to 10 oz./gal., temperature 160 to 180 F.,

4) 30-second cold water rinse,

5) l to 10-minute immersion in an acidic aqueous potassiumperoxydiphosphate solution at a temperature about 60 to about 170 F. todesmut and deoxidize the aluminum,

16) 30-second cold water rinse, and

7) subsequent finishing operations such as: anodizing,

chromating, etc.

A similar process in which the etching step is not emloyed comprises thefollowing steps:

PROCESS II 1) 3 to S-minutes immersion in an alkaline non-etch aluminumsoak cleaner at a concentration of 8 to 10 02/ gal. and at a temperatureof about 160 to 180 F.,

2) 30-second cold water rinse,

3) 1 to S-minute immersion in an acidic aqueous potassiumperoxydiphosphate solution at a temperature of about 60 to about 170 F.,to deoxidize the aluminum,

4) 30-second cold water rinse, and

5) subsequent finishing operations such as: anodizing,

chromating, etc.

Generally, the metal surface is immersed in the acidic ,queousperoxydiphosphate bath for about 1 to about 0 minutes or more andpreferably for about 1 to about 1 minutes. A useful deoxidizer-desmuttersolution not nly must remove smut and deoxidize the aluminum but .lllStalso not have a detrimental effect on the metal surace with extendedimmersion times. These requqirements re met in the novel acidicperoxydiphosphate solutions f this invention.

In another aspect, this invention relates to dry comositions which canbe dissolved with mixing in water form deoxidizing and desmuttingsolutions of the type reviously described. The dry compositions of thisinention comprise (l) a water soluble peroxydiphosphate alt selectedfrom the group consisting of ammonium perxydiphosphate, an alkali metalperoxydiphosphate and n alkaline earth metal peroxydiphosphate, (2) anacid alt of sulfuric acid and, optionally, a soluble fluoride salt.Generally, the novel dry compositions of this invention will contain thefollowing ingredients in approximate percentages indicated below:

Ingredients: Percent by weight Peroxydiphosphate salt 520 Acid salt ofsulfuric acid 77-95 Fluoride salt 0-3 Any of the peroxydiphosphatesalts, acid salts of sulfuric acid, and fluoride saltspreviouslydescribed in connection with the description of the novel deoxidizingand desmutting solutions of this invention can be employed in preparingthe novel dry compositions.

The pH of the aqueous solution prepared from the dry compositions mustbe less than 3.0 if the resulting solution is to operate effectively asa deoxidizing and desmutting composition. However, if adjustment of thepH is required, it can be conveniently carried out through the additionof sulfuric acid in any needed amount.

Dry powder compositions offer a number of advantages over the liquidcompositions especially with regard to easier handling and lowershipping weights. Further, the use of such dry compositions offers theadditional advantage of elimination of the majority of the weighing outor measuring operations thus further reducing the possibility of faultymake-up.

The following examples illustrate various embodiments of this inventionand are to be considered not limitative.

Example I An aqueous solution containing the following ingredients inthe amounts indicated, in addition to water, was prepared:

Potassium peroxydiphosphate (K P O )--120 g./l. I Sulfuric acid (66B.)40 ml./l. pH 3.0

Aluminum objects prepared from Type '7075 aluminum alloy (Analysis: 1.6%Cu, 2.5% Mg., 5.6% Zn,

7 0.2% Cr-balance Al plus impurities) were immersed in a non-etchaluminum soak cleaner having a concentration of 8 oz./ gal. at 170 F.,rinsed in cold water, immersed in an alkaline etchant at a concentrationof 10 oz./gal. at F. for 3 minutes during which time a heavy dark smutdeveloped on the surface of the aluminum objects, again rinsed in coldwater, immersed in the above-described solution of potassiumperoxydiphosphate at a temperature of 70 F. for 3 minutes; and thenrinsed for 30 seconds in cold water. The thus-treated aluminum objectsexhibited light and smut-free surfaces which provide an excellent basefor subsequent finishing operations such as painting, dyeing,chromating, etc.

Example II In this example an aqueous solution having the followingcomposition is employed in treating the surfaces of aluminum objects:

Lithium peroxydiphosphate (Li P O )--lO5 g./1. Sulfuric acid (66 B.)60ml./l. pH 3.0

Utilizing the same procedure and cleaning and etching solutions utilizedin Example I, aluminum objects of Type 2024 alloy (Analysis: 4.5% Cu.,0.6% Mn, 1.5% Mgbalance Al plus impurities) are desmutted and deoxidizedin the above-described lithium peroxydiphosphate solution. The resultingaluminum alloy objects possess light surfaces completely free of smutwhich are highly satisfactory for further finishing.

Example 111 In this example articles made of an aluminum alloy having asubstantial silicon content are deoxidized and 6 desmutted using anaqueous solution of the following com- What is claimed is: position: 1.A composition for desmutting and deoxidizing aluminum and aluminumalloys consisting essentially of a mig i l g ggg g ZE g f f 140 dryadmixture of from about to 20 weight percent of Sulfuric acid mL/L 5 acompound selected from the group consisting of an P alkali metalperoxydiphosphate, an alkallne earth metal peroxydiphosphate, andammonium peroxydiphosphate; Aluminum articles maHllfamI edf1'm p 6061alloy from about 77 to 95 weight percent of an acid salt of (Analysis:0.25% Cu, 0.6% S1, 1.0% Mg and sulfuric acid and from 0 to about 3.0weight percent of Crbalance vAl plus impurities) are first cleaned byim- 10 water-soluble fluoride alt,

mersion for 5 minutes at 160 F. in an alkaline non- The Composition ofclaim 1 wherein the Said etch aluminum soak cleaner at a concentrationof 8.5 pound is potassium peroxydiphosphate. oz./gal., rinsed 1n coldwater for 30 seconds, immersed 3. The composition of claim 1 wherein theSaid acid in the peroxydiphosphate solution previously prepared in Saltof Sulfuric acid is sodium bisulfate a thls example for mmutes at 80 and"used agant for 4. The composition of claim 1 wherein the said fluorideabout 30 seconds in cold water. The thus-treated articles salt is sodiumfluoride.

exhibit aluminum surfaces which are of excellent appear- A compositionaccording to claim 1 consisting s gq i g q gmshmg operatlons Suchsentially of about 15.3 Weight percent of potassium peroxyas P osp a mglppmg e diphosphate with the balance being sodium bisulfate.

E l 1V XII 6. A deoxidizing and desmutting solution for aluminum andaluminum alloys consisting essentially, in addition to water: (1) asoluble peroxydiphosphate compound selected from the group consisting ofammonium peroxydiphosphate, an alkali metal peroxydiphosphate and an Inthese examples articles prepared from Type 6061 and 6063 aluminum alloyswhich contain substantial quantities of silicon were cleaned, etched andthen treated at a temperature of 72 F. in an acidic aqueousperoxydiphosphate solution in the same manner as described in alkalineearth metal p p p ill of Example I. Pertinent data relating to theacidic peroxyb011t 18 1 t0 SaturatlOIl; a Soluble flu ride Saltdiphosphate compositions utilized in these examples is in amountsufficlent to provide a fluoride ion concentrashown in Table 1 whichfollows: tion in the solution of from 0 to about 6 -g./l. and (3) anTABLE 1 Example Number IV V VI VII VIII IX X XI XII Deoxidizing solutioncomposition: 1

Potassium peroxydiphosphate (g./

1 Ingredients shown are in addition to water.

In each instance the surfaces of the resulting aluminum acid materialselected from the group consisting of sul articles, which were smut-freeand of light appearance, furic, phosphoric and sulfamic acid, the acidsalts thereof, provided a highly satisfactory base for further finishingand mixtures of the said acids and acid salts, in amount operations.sufficient to provide a solution pH of not more than 3.0.

Example XIII 7. The solution of claim 6 wherein the saidperoxydiphosphate compound is potassium peroxydiphosphate.

8. The solution of claim 6 wherein the said acid is sulfuric acid.

9. The solution of claim 6 wherein said fluoride salt is sodiumfluoride.

10. A solution according to claim 6 consisting essentially, in additionto water, potassium peroxydiphosphate and sulfuric acid.

11. A process for deoxidizing and desmutting aluminum and aluminum alloyarticles which comprises treating said articles by immersing them for aperiod of about 1 to about 10 minutes at a temperature of about 60 F. toabout 170 F. in a solution consisting essentially, in addition to water:(1) a soluble peroxydiphosphate compound selected from the groupconsisting of ammonium peroxydiphosphate, an alkali metalperoxydiphosphate,

A dry mixture is prepared by admixing 100 g. of finelydivided sodiumbisulfate and 19 g. of finely-divided sodium bisulfate and 18 g. offinely-divided potassium peroxydiphosphate. This composition, whenthoroughly mixed, can be stored for long periods of time in appropriateshipping containers without hazard and without deterioration.

An aqueous solution is prepared containing 118 g. of the above-describeddry mix per liter (pH about 1.6). This solution is employed indesmutting and deoxidizing articles prepared from Type 7075 aluminumalloy in the same manner as set forth in Example I. The thus-treatedarticles possess a light and smut-free surface highly suitable forfurther operations including anodizing, dyeing, painting, etc.

Example XIV and an alkaline earth metal peroxydiphosphate, in amount Anacidic aqueous composition containing, in addition of about 18 g./l. upto saturation; (2) a soluble fluoride to water, 120 g./l. of potassiumperoxydiphosphate and salt in amount sufiicient to provide a fluorideion con- 40 mls. of sulfuric acid (66 B.) is prepared. centration in thesolution of from 0 to about 6 .g./l. and Aluminum articles constructedof Type 2024 and 7075 (3) an acid material selected from the groupconsisting aluminum alloys are first alkaline cleaned, rinsed and ofsulfuric, phosphoric and sulfamic acid, and the acid then immersed inthe peroxydiphosphate solution of this salts thereof and mixtures of thesaid acid and acid salts,

example for 4 minutes at a temperature of 90 F. to give in amountsuflicient to provide a solution pH of not more smut-free articles. than3.0.

8 References Cited UNITED STATES PATENTS 7/1964 Grunwald 134-3 3/1968Grunwald 252186 X MAYER WEINBLATI, Primary Examiner U.S. Cl. X.R.

